Process for the production of urea and ammonium salts



July 20, 1937.

LAWRENCE ET AL PROCESS FOR THE:` PRODUCTION OF URBA AND AMMONIUM SALTS PROCESS FOR THE PRODUCTION OF UREA AND AMMONIUM SALTS l 0,954 w20 -602 fw/3 CARBON wax/0,5 G45-` NH4 Nq, Jazar/0N l ATTQRNEY v Patented `Iuly 20, 1937 UNITED STATES PATENT OFFICE PROCESS FOR THE PRODUCTION OF UREA I AND AMIVIONIUM SALTS of lNew York Application September 13,1933, Serial No. 689,246

15 Claims.

'Ihis invention relates `to a process for the production of urea and ammonium salts such as ammonium carbonates. ammonium chloride, ammonium nitrate or ammonium sulfate.l

It is known to produce urea by heating ammonia and carbon dioxide `under pressure to convert the materials into urea in accordance with the following equation:

present principally in the form of ammonium carbamate or carbonate. It is frequently desir- 20 able, furthermore, to employ in the synthesis of urea an excess either of ammonia or of carbon dioxide over that corresponding to the stoichiometric proportions for the formation of urea and, in such a case, the reaction product from 25 the urea synthesis may contain uncombined ammonia or carbon dioxide in addition toA ammonium carbamate or carbonate.

One of the major problems in developing a commercially satisfactory vmethod for the synthesis of urea from ammonia and carbon dioxide has been the provision of satisfactory methods forrecoveringthe unconverted ammonia and carbon dioxide from the eiiiuent of the urea autoclave. Heretofore it has been proposed to heat 35 the eilluent to drive out the unconverted ammonia and carbon dioxide and return these materials to the autoclave .for the production of further quantities of urea. In one process, the ammonia. and carbon dioxide distilled from the 40 autoclave eiiluent are directly compressed without separation for return to the autoclave. This compression, however must be carried out at high temperatures to avoid the formation of solid ammonium carbamate, which high tem- 45 perature compression involvesA mechanical difficulties and low eflciencies of the compression step. It has also been proposed to separate the ammonia from the carbon dioxide as, for example, by selective absorption of the ammonia,

50 and then recovering the gases separately and separately recompressing them and returning them to the urea synthesis autoclave. Such a mode of operation. however, is costly and adds appreciably to the cost of the urea synthesis.

55 It is an object of this invention to provide a (Cl. 26o-125) method for the production of valuable ammonium salts from the unconverted ammonia in the urea synthesis eilluent which obviates the necessity of recovering both the ammonia, and carbon dioxide for re-use in the urea synthesis process itself and in which the value of the ammonium salt compensates for the cost involved .inits production. It is furthermore an object of this invention to provide a novel method for the eective `elimination of unconverted ammonia and carbon dioxide from a urea. synthesis eiiiuent and the recovery from the gaseous mixture obtained in thetreatment of the urea. synthesis efiluent of ammonia in the form of an ani-'- monium salt anda concentrated carbon dioxide gas whichmay be readily and economically returned to the urea synthesis.

In carrying out the process of this invention, ammonia and carbon dioxide are heated under pressure to a temperature promoting the forma- 2O tion of urea. The resulting product is passed in contact with an inert gas such as air to strip unconverted ammonia and carbon dioxide from the product. The mixture of gases thus obtained is then treated to separate the ammonia and carbon dioxide from the inert gas. This separation may be accomplished by cooling the gases to a temperature at which the ammonia and carbon dioxide combine tc form ammonium carbonate-carbamate; i. e., a product which may 30 consist principally of normal ammonium carbonate, ammonium bicarbonate or of ammonium carbamate, together with more or less of the other named compounds, the exact composition yof the product depending upon the ratio of ammonia and carbon dioxide in the cooled gas and the proportion of Water combined with the ammonia and carbon dioxide. This cooling of the gases to fdrm ammonium carbonate-Carbamate may be accomplished by passing the gases in 40 contact with a solution of ammonium carbonate. Or the gases may be passed in contact with a solution of .an ammonium salt such as ammonium nitrate, ammonium sulfate, and the like, to.form a solution of ammonium carbonate. It is apparent that in order to accomplish this separation of the ammonium carbonate-carbamate or ammonium carbonate from the inert gas, the inert gas used is one which, like air, is not condensed at temperatures at which the gaseous ammonia and carbon dioxide combine to form solid ammonium carbonate-carbamate or, in the presence of Water, a-solution of ammoniumcarbonate. The solution of ammonium carbonate. or the ammonium carbamate-car- Cil bonate solid obtained as described, yis.- i;reateud' with an acid such as nitric acid, sulfuric acid,`

` dissolved in the solution and it is then carbonated by absorbing carbon dioxide in it to precipitate sodium bicarbonate. The sodium bicarbonate may be filtered from the solution containing ammoniumv chloride, ammonium nitrate or ammonium sulfate andv heated to evolve a concentrated carbon dioxide gas and form the normal sodium carbonate. In case the ammonium carbonate solution in which the sodium salt is dissolved originally contains ammonium bicarbonate, the carbonating of the solution obtained after dissolving the sodium salt may be omitted or materially curtailed.

Ammonium sulfate may also be prepared in accordance with this invention by mixing the ammonium carbonate solution obtained as described above With finely divided calcium sulfate, whereby calcium carbonate is precipitated and a solution of ammonium sulfate formed. After separation of the calcium carbonate from the solution the ammonium sulfate may be recovered by concentrating and crystallizing the ammonium sulfate from the solution. The calcium carbonate may then be decomposed with an acid, for example, nitric acid, to recover the carbon dioxide.

The process of this invention further comprises the modifications of processes described above which involve the direct absorption of the ammonia and carbon dioxide in the gases obtained by distilling the effluent from a urea synthesis autoclave in solutions of sodium salts such as sodium chloride, sodium nitrate or sodium sulfate, or a suspension of calcium sulfate whereby ammonium chloride, ammonium nitrateor ammonium i sulfate is directly formed in the solution. Such a procedure simplifies the production of these ammonium salts by not requiring a separate treatment of the ammonia and carbon dioxide gas for the intermediate production of an ammonium carbonate solution.

In the accompanying drawings, Fig.'1 shows diagrammatically a process for the production of urea and of ammonium chloride, and Fig. 2 a process for the production of urea and ammonium nitrate, which are illustrative of this invention.

Referring to Fig. 1 of the drawings, ammonia gas is compressed and liquefied in an ammonia liquefying system I and carbon dioxide is compressed and liquefied in a carbon dioxide liquefying system 2. The liquid ammonia and liquid carbon dioxide in the proportions of about 2 mols of ammonia for every 1 mol. of carbon dioxide are continuously passed into an autoclave 3 in which the reaction mixture is heated at a temperature of about 150 to 200. C. while maintaining it under a pressure of -10,() to 300 atmospheres. The ammonia and carbon dioxide react to form urea and a product containing this ma.- terial, together with water and unconverted ammonia and carbon dioxide, is continuously withdrawn from the autoclave and passed into. the

top` of a stripper 4, where it is passed in direct contact with air which is introduced into the bottom of stripper 4.l Stripper 4 is operated at a pressure materially below that of autoclave 3;

`for example, a pressure of a few pounds gauge,

and as the effluent from the autoclave-at an elevated temperature is introduced into the stripper at the lower pressures, ammonia and carbon dioxide are `evolved from the melt. The liquor or melt in the top of the stripper may have a temperature of, for example C., which is below the boiling point of the liquor. The air introduced into the stripper may be preheated or the stripper may contain heating coils whereby the heat,required for the evolution of the unconverted carbon dioxide and ammonia in addition to the heat already contained in the autoclave eflluent may be supplied. Also, steam may be introduced with the air entering the bottom of the stripper to supply a desired amount of heat. If desired, this steam may be introduced into thestripper at an intermediate point instead of into the bottom of the stripper. n

A solution of urea substantially free from ammonia and carbon dioxide flows off from the bottom of stripper 4 and may be treated in any desired manner for the recovery of the urea. A gaseous mixture of air, ammonia and carbon dioxide is drawn off from the top of the stripper and conducted to a cooler or absorber 5 while maintaining the gases at a temperature of, for example, 75 vC., which is above the temperature at which the ammonia and carbon dioxide would combine to precipitate a solid ammonium carbamate-carbonate in the pipes leading from the stripper to the absorber. Absorber 5 contains an' aqueous solution of ammonium carbonate which is maintained at a temperature of about 40 C. This temperature regulation may be accomplished by circulating cooling water through coils submerged in the ammonium carbonate solution. The ammonia and carbon dioxide are absorbed in the ammonium carbonate solution and water is continuously added at a rate sucient to supply vthe desired proportion of water for combination with the ammonia and carbon dioxide to form ammonium carbonate and to give a solution of a desired composition. The air separated from the ammonia and carbon dioxide may be returned from absorber 5 for` reuse in stripper 4.

The ammonium carbonate solution is passed from absorber 5 into a carbonating column 6 into which sodium chloride is introduced and dissolved in the ammonium carbonate solution and carbon dioxide is passed in contact with the resulting solution to precipitate sodium bicarbonate. 'I'he slurry of sodium bicarbonate and solution containing ammbnium chloride is passed to a filter l for removal of the sodium bicarbonate, and this is heated in a kiln 8 to evolve carbon dioxide and to form soda ash (sodium carbonate). The carbon dioxide evolved in kiln 8 may be returned to liquefying system 2 and thence to the `urea synthesis or may in part be returned to carbonating column B for treatment of further quantities' of ammonium carbonatesodium chloride solutions. If desired, a relatively dilute carbon dioxide gas may be employed for the treatment of the liquor in carbonating co1- umn 6,"and the carbon dioxide thus absorbed I may be recovered from the concentrated solution. be recovered from the resulting solution bycooli Other ammonium salts such as ammonium nif- Vtratte or ammonium sulfate may be obtained by dissolving the corresponding sodium 'salt in the ammonium carbonate solution introduced into carbonating column 6 in the process above described. It is also possible to omit the carbonating of the solution by forming in absorber 5 a solution of ammoniumbicarbonate. 'I'his may be accomplished by introducing into the absorber carbon dioxide in desired proportion in addition to the carbon dioxide obtained in the gases coming from stripper 4, or by employing in the urea synthesis an excess of carbon dioxide over the proportions of 2NH3 to lCOz so'that the gases from stripper 4 contain ammonia and carbon dioxide in the ratio of lNHa to 1G02.

Instead of4 treating the ammonium carbonate solution from absorber 5 in the manner described above, this solution containing about 30% (NH4)2CO3 at about.40 C. may be agitated with nely divided gypsum (CaSO4.2H2O) in the proportions of about 100 parts oi the ammonium carbonate solution to about 53 parts of the gypsum. The ammonium' carbonate and calcium sulfate react to form' ammonium sulfate and calcium carbonate. 'I'he calcium carbonate is illtered from the solution of ammonium sulfate and the solution evaporated and ammonium sulfate crystallized out. The calcium carbonate may then be reacted With nitric acid to obtain calcium nitrate with the evolution of carbon dioxide gas which is returned to the urea synthesis.

Ii desired, the gases containing ammonia and carbon dioxide from stripper 4 may be passed directly into a suspension of iinely divided gypsum in water to form ammonium carbonate and ammonium sulfate. Either natural gypsum or a byproduct gypsum such as is obtained by treating phosphate rock with nitric acid and precipitating the calcium by addition of ammonium sulfate, may be utilized for the production of the ammonium sulfate. Other ammonium salts such as ammonium nitrate or ammonium chloride may also be obtained by treating the corresponding calcium salt (calcium nitrate or calcium chloride) with the ammonium carbonate solution to precipitate calcium carbonate and leave a solution of ammonium nitrate or ammonium chloride. It is also sometimes advantageous, Where an ammonium salt is to be formed from a sodium salt, to directly absorb the ammonia and carbon dioxide in the sodium salt solution, for example 'sodium chloride solution, and then to carbonate the resulting solution to precipitate out sodium bicarbonate.

Instead of treating the ammonium carbonate solution from absorber 5 for the conversion of the ammonium carbonate into ammonium sulfate, ammonium nitrate or ammonium chloride,- ammonium carbonate itself may be recovered as asolid from this solution. For example, the ammonium carbonate solution at 40 C.. from absorber 5'may be cooled to 25 C. to crystallize ammonium carbo-nate therefrom. The crystalline ammonium carbonate is separated from the mother liquor and the latter returned to absorber E for the treatment of further quantities of gas from stripper 4. Ammonium bicarbonate may be obtained by introducing additional CO2 into the gas mixture coming from stripper 4 so that the gas contains about 1 mol. ammonia to 1 mol. carbon dioxide. This gas is then passed in contact with an ammonium bicarbonate solution at about 25 C. and solid ammonium carbonate may ing.

Fig. 2 illustrates a process for the production oi! ammonium nitrate in accordance with this invention. In this process aniammonia liqueiying system I0, carbon dioxide llqueiying system II, urea autoclave I2, and stripper I3 are operated as in carrying out the process 4of Fig. 1 described above. The gases from stripper t3 are passed into an'absorber I4 where they are treated with an aqueous solution o! ammonium nitrate containing about 50% NH4NO3 maintained at a temperature'of about 50 C. The ammonium nitrate solution cools the gase's from stripper I3 and absorbs the ammonia. and carbon dioxide. The solution is treated until it is substantially saturated with ammonium carbamate-carbonate. 'I'he resulting solution is withdrawn to a ne tralizlng vessel I5, where it is treated with 40 0 nitric acid to form ammonium nitrate and evolve -a concentrated carbon dioxide gas, which is returned to liquefying system II. The ammonium nitrate solution, which may be neutral or slightly acid, is then evaporated in an evaporator I6 to obtain a concentrated solution from which solid ammonium nitrate may be recovered by cooling or the solution may be evaporated under a reduced pressure to crystallization in evaporator I8 and the crystals recovered by filtration. A portion of the solution from neutralizing vessel I5 may be returned to absorber I4 for recovery of ammonia and carbon dioxide from the gases passed through the absorber. The process ofv Fig. 2 may be operated continuously, if desired. If

desired, the neutralization of the .ammonium carbamate-carbonate solution formed in absorber I4 may be accomplished by introducing the acid into the solution in the absorber itself, in which case the absorption of the ammonia and carbon dioxide may be continuously carried out by employing duplicate absorption vessels I4 and while one is serving for the treatment of the gases from the stripper, the solution in the other isI the reaction imposed by the processes heretofore required for recovery of unconverted ammonia and carbon dioxide. For example, a considerable excess of ammonia may be employed in the urea vsynthesis step itself with the attendant advantages derivable therefrom, and this ammonia economically yrecovered as a. valuable ammonia salt product. A furtherv advantage of the `process of this invention which uses an inert gas such as air for, stripping the unconverted ammonia and carbon dioxide from urea synthesis melts, is with respect to the completeness of recovery of these materials from the melt. While the hot product leaving the urea synthesis autoclave, upon reduction of the pressure, will evolve a considerable proportion of the ammonia and carbon dioxide, the complete stripping of the melt by means of heat alone involves a supply of considerable quantities .of heat atA elevated temperatures.

urea content. By employing an inert gasin the stripping operation, heat at lower temperatures,

-. which are below the boiling point of the melt itself may be utilized. This is not only economical but has the advantage of decreasing the losses, due to decomposition of urea in the meltand at the same timethe melt may be substantially completely freed of uncombined ammonia and carbon. dioxide.

. We claim: Y

l. The process for the production of 'urea and an ammonium salt which comprises heating ammonia and carbon dioxide at a urea-forming temperature and pressure, passing the resulting product containing urea, ammonia and carbon dioxide in contact with an inert 'gas substantially free from ammonia and carbon dioxide at a temperature, below the boiling point of said product, at which the gas strips from the product ammonia and carbon dioxide, said inert gas being one which is not condensed at temperatures at which gaseous ammonia and carbon ldioxide combine to forni ammonium carbonatecarbamate, cooling the resulting gaseous mixture containing ammonia and carbon dioxide to recover an ammonium carbamate-carbonate material therefrom, separating said carbamatekcarbonate material from the inert gas and treating the thus separated material to form an ammonium salt and carbon dioxide gas therefrom. x

2. The process for the production of urea and an ammonium salt which comprises heating ammonia and carbon dioxide at a urea-forming temperature and pressure, passing the resulting product containing urea, ammonia and carbon dioxidev in contact with an inert gas substantially free from ammonia and carbon dioxide at a temperature, below the boiling point of said product, at which the gas strips from the product'ammonia and carbon dioxide, said inert gas being one which is not condensed at temperatures at which gaseous ammonia and carbon dioxide combine to form ammonium carbonatecarbamate, passing the resulting mixture of gases in contact with an aqueous liquor at a temperature at which the ammonia and carbon dioxide are absorbed in the liquor, separating the resulting solution from said inert gas, treating the solution to convert its ammonia content into an ammonium salt and recover carbon dioxide as a gas, and reacting the recovered carbon dioxide with ammonia to form urea.

3. The process for vthe production of urea and an ammonium salt which comprises heating ammonia and carbon dioxide at a urea-forming temperature and pressure, passing the resulting product containing urea, ammonia and carbon dioxide in contact with an inert gas substantially free from ammonia and carbon dioxide at a temperature, below the boiling point of said product, at which the gas strips from the product ammonia and carbon dioxide, said inert gas being one which is not condensed at temperatures at which gaseous ammonia and carbon dioxide combine to form ammonium carbonate- .carbamata passing the resulting gaseous mixture containing ammonia and carbon dioxide in contact with an aqueous liquor to absorb ammonia and carbon dioxide from said gases, separating the resulting solution from the inert gas form the corresponding ammonium salt and evolve concentrated carbon dioxide gas.

4. The process for the production of urea and an ammonium salt which comprises heating ammonia and carbon dioxide at a urea-forming temperature and pressure, passing the resulting product containing urea, ammonia and carbon gas being one which is not condensed at temperatures at which gaseous ammonia and carbon dioxide combine to form ammonium carbonatecarbamate, cooling said mixture of gases to a temperature at which the ammonia and carbon dioxide combine to form ammonium carbonatec'arbamate, separating said ammonium carbonate-carbamate from said inert gas, and treating the thus separated carbonate-carbamate with an acid to convert it into an ammonium salt and carbon dioxide gas.

5. The processior the production of urea and an ammonium salt which comprises heating ammonia and carbon dioxide at a urea-forming temperature and pressure, passing the resulting product containing urea, ammonia and carbon dioxide in contact with an inert gas substantially free from ammonia and carbon dioxide at a temperature, below the boiling point oi said product, at which the gas strips from the product ammonia and carbon dioxide, said inert gas being one which is not condensed at temperatures at which gaseous ammonia and carbon dioxide combine to form ammonium carbonatecarbamate, passing the gaseous mixture containing ammonia and carbon dioxide in contact with an aqueous solution of an ammonium salt at a temperature at which the ammonia and carbon dioxide combine to form ammonium carbonate, separating the resulting solution of ammonium carbonate from the inert gas and introducing an acid into the solution containing ammonium carbonate to form the corresponding ammonium salt and to evolve concentrated carbon dioxide gas.

6. The process for the production of urea and ammonium nitrate which comprises heating ammonia and carbon dioxide at a urea-forming temperature and pressure, passing the resulting product'containing urea, ammonia and carbon dioxide in contact with air at a temperature,

and introducing an acid into the solution to below the boiling point of said product, at which v the air strips unconverted ammonia and carbon dioxide from the product while maintaining the resulting mixture of air, ammonia and, carbon dioxide at a temperature above that at which the ammonia and carbon dioxide combine to form ammonium carbonate, passing the resulting gases in contact with an aqueous solution of ammonium nitrate at a temperature at which the ammonia. and carbon dioxide combine to form ammonium carbonate, separating the resulting solution from the air, neutralizing the solution containing ammonium carbonate with nitric acid and reacting the carbon dioxide evolved from the solution with additional am monia for the production of urea therefrom.

7. The process for the production of urea and an vammonium salt which comprises heating amperature, beiow the boiling point of said product.

at which thegas strips from theproduct ammonia andcarbon dioxide, said inert gas being one which is not condensed at temperatures at which gaseous ammonia and carbon dioxide com- .bine to form ammonium carbonate-carbamate,

said inert gas being one which is not condensed at temperatures at which gaseous ammonia and carbon dioxide combine to form ammonium 'carbonate-carbamate, cooling the resulting mixture of gases in contact with a solution of ammonium carbamate-carbonate to absorb ammonia and carbon dioxide from the gases, separating the resulting solution from the'inert gas and reacting the resulting solution with nely divided calcium sulfate to forni ammonium sulfate and calcium carbonate.

8. The process for the production of urea sodium bicarbonate and ammonium chloride which comprises heating ammonia and carbon dioxide in the proportions of about 2 mois of ammonia for every 1 mol. of carbon dioxide at a urea-forming temperature and pressure, passing the resulting product containing urea, ammonia and carbon dioxide in contact with air at a temperature, below the boiling point of said product, at which the air strips unconverted ammonia and carbon dioxide from the product while maintaining the resulting mixture of air, ammonia and carbon dioxide at a temperature above that at which the ammonia and carbon dioxide combine to form ammonium carbonate, passing the resulting gases in contact with an aqueous solution of ammonium carbonate at a temperature at which the ammonia and carbon dioxide combine to form a carbonate of ammonia and reacting thecarbonate of ammonia with sodium chloride to form sodium bicarbonate and ammonium chloride.

9. 'I'he process for the production of urea sodium bicarbonatey and ammonium chloride which comprises heating ammonia and carbon dioxide in the proportions of about 2 mols of ammonia for every 1 mol. of carbon dioxide at a urea-forming temperature and pressure, passing the resulting product containing urea, ammonia and carbon dioxide in contact with air ata temperature, below the boiling point of said product, at which the air strips unconverted ammonia and carbon dioxide from the product while maintaining the resulting mixture of air, ammonia and carbon dioxide at a temperature above that at which the ammonia and carbon dioxide combine to form ammonium carbonate, passing the resulting gases in contact with an aqueous solution of ammonium carbonate at a temperature at which the ammonia and carbon dioxide combine to form a carbonate of ammonia, dissolving sodium chloride in the solution of carbonate of ammonia thus prepared and carbonating the solution to precipitate sodium bicarbonate therefrom, separating the precipitated sodium bicarbonate from the solution containing ammonium chloride, heating the sodium bicarbonate tolevolve carbon dioxide gas therefrom and reacting the carbon dioxide thus obtained with ammoniaifor the production of urea therefrom.

`10. The process for the production of urea and an ammonium salt which comprises heating ammonia and carbon dioxidevat a urea-forming temperature and pressure, passing the resulting product containing urea, ammonia and carbon dioxide at a pressure ,of a few pounds gauge in contact with air at a temperature, below the boiling point of said product at which the air strips therefrom ammonia and carbon dioxide, maintaining the resulting mixture of gases while in contact with said product andsubsequent thereto at a temperature at which the ammonia and carbon dioxide remain in the gaseous phase, cooling said mixture of gases after removal from contact with said product to a temperature at which the ammonia and carbon dioxide combine to form ammonium carbonate-carbamate, separating the ammonium carbonate-carbamate from the air and treating said ammonium carbonate-carb'amate to form an ammonium salt and concentrated carbon dioxide gas therefrom.

11. 'I'he process for the productionof urea and an ammonium salt which comprises heating ammonia and` carbon dioxide at a urea-frmlng temperature and pressure, passing the resulting melt containing urea, ammonia and carbon dioxide atI an pressure of a few pounds gauge in contact with a stream of air which is continuously recycled in a gas circulatory system in which the melt is treated with-the air at a temperature, below the boiling point of the melt, at which the air strips therefrom ammonia and carbon dioxide and the resulting mixture of gases is subsequently cooled to a temperature at which the ammonia and carbon dioxide combine to form an ammonium carbonate-carbamate material, removing said material from contact with the air in said circulatory system, and then treating the am. monium carbonate-carbamate material to form an ammonium salt and concentrated carbon dioxide gas therefrom.'

12. The process for the production of urea and an ammoniumA salt which comprises heating ammonia and carbon dioxide at a urea-forming temperature and pressure, passing the resulting product containing urea, ammonia and carbon dioxide at a pressure of a few pounds gauge in contact with a stream of an inert gas which is continuously recycled in a gas circulatory system in Whichthe melt is treated with the inert gas at a temperature, below the boiling point of the melt, at which the gas strips therefrom ammonia. and carbon dioxide and the resulting mixture of gases is subsequently cooled to a temperature at which the ammonia and carbon dioxide combine to form an ammonium carbonatecarbamate material, removing said material from contact with the inert gas in said circulatory system, and then treating the ammonium carbonate-carbamate material to form an ammonium salt and concentrated carbon dioxide gas therefrom.

13. The process for the production of urea and an ammonium salt which comprisesheating ammonia and carbon dioxide at a urea-forming temperature and pressure, passing the resulting product containing urea, ammonia and carbon dioxide at a pressure of a .few pounds gauge in contact with a stream of an inert gas which is continuously recycled in a gas circulatory system in which the melt is treated with the inert gas at a temperature, below the boiling point of the dioxide from said gases, separating the resulting i solution from the inert gas and introducing an 14. The process for the production of urea and an ammonium salt which comprises heating ammonia and carbon dioxide at a urea-.forming temperature, passing the resulting product containing urea, ammonia 4and carbon dioxide in contact with an inert gas substantially free from ammonia and carbon dioxide at a temperature, below the boiling point of said product, at which the gas strips fromy the product ammonia and carbon dioxide, said inert gas being one which is not condensedA at temperatures at which gaseous ammonia and carbon dioxidecombine to form ammonium carbonate-darbamate, and cooling the resulting gaseous mixture containing ammonia and carbon dioxide to recover an ammo- Vnium carbamate-carbonate material therefrom.

15 The process' for the production of urea and an ammonium salt which comprises heating ammonia and carbon dioxide at a urea-forming temperature, passing the resulting product containing urea, ammonia and carbon dioxide in contact with an inert gas substantially free from ammonia and carbon dioxide at a temperature, below the boiling point of said product, at which "the gas strips from the product ammonia and carbon dioxide, said inert gas being one which is not condensed at temperatures at which gaseous ammonia and carbon dioxide combine to form ammonium carbonate-carbamate, passing the resulting mixture of gases in contact with an aqueous liquor at a temperature at which both the ammonia and carbon dioxide are absorbed in the liquor to form an ammonium carbamate-carbonate material, separating the resulting solution from the inert gas and treating the thus separated solution to convert its ammonia content into an ammonium salt of the group consisting of ammonium sulfate, ammonium nitrate, ammonium chloride and ammonium phosphate.

' CHARLES K. LAWRENCE.

HERMAN A. BEEKHUIS, Jn. 

